The legalization of marijuana in Alaska, Colorado, Oregon, and Washington is the most dramatic change in U.S. substance abuse policy since the end of Prohibition. These states are implementing regulatory and enforcement systems for the retail sales of recreational marijuana to adults 21 years or older, akin to state controls on the sale of alcohol. In 2013, the U.S. Department of Justice (DOJ) issued directives that it would monitor whether these states implemented strong and effective regulatory and enforcement systems that among other DOJ priorities, prevented distribution of marijuana to youth. A retail sales intervention that has been effective at reducing illegal alcohol sales to minors (and intoxicated patrons) is alcoholic beverage server training (or Responsible Beverage Service training - RBS). Recently, Colorado enacted a law for incentivized responsible marijuana vendor (RMV) training, Oregon will require RMV training, and Washington proposes to incentivize it. In SBIR Phase I research, our team established the feasibility of creating and evaluating an online RMV training by a) exploring the concept/content of RMV with owners/managers and clerks in retail outlets and state and local regulators and enforcement officials; b) examining under-age sales with owners/managers, clerks, and underage individuals; c) developing and evaluating a prototype RMV training, Way To Tend, in an outline and storyboards and by programming one module with retail outlet personnel and local officials; d) identifying licensed marijuana retail outlets eligible for a randomized trial; and e) estimating current refusal rates of sales of marijuana to minors with a pseudo-patron (PP) buyer assessment. An Expert Advisory Board (EAB) comprised of state and local regulators, licensed retail cannabis sellers, and experts in responsible beverage service from these states confirmed the feasibility of the Way To Tend training. In this SBIR Phase II application, we propose to 1) produce the Way To Tend responsible marijuana vendor (RMV) training presenting retail marijuana sales laws, methods for preventing sales to minors (i.e., ID checking and preventing third party sales), the health effects of marijuana (e.g., driving under the influence; fetal exposure; dosing; and safe storage), and rules of the trade (e.g., tracking and safety procedures and sales to intoxicated patrons) and 2) conduct a randomized trial of Way To Tend in a sample of 150 retail marijuana outlets in Colorado, Oregon and Washington against control outlets who receive usual and customary (UC) training and examine Way To Tend's impact on RMV outcomes (refusals to PP without apparently valid IDs). The long-term objectives of the SBIR research are urgently needed and extremely significant as increased drug availability is linked to marijuana initiation. The proposed research will have a very large impact. Our effective RMV training by a third-party (not the cannabis industry) will be a first-of-its-kind for a highly uniqe circumstance, the first legal U.S. retail marijuana markets. The commercial potential for Way To Tend is untapped and potentially very large, for the market is poised to grow tremendously as more states consider legalization of marijuana.